How do nodes find peers without bootnodes?

Question

I know once a peer is added, it also communicates its own peers. But how is the first peer added? Do the nodes (Geth & Parity) have built-in bootnodes? Or is there a scanning method of some kind?

Thanks,

Answer 1

yes there is some built-in bootstrap nodes you could check the code in github :

Geth : https://github.com/ethereum/go-ethereum/blob/ff2c966e7f0550f4c0cb2b482d1af3064e6db0fe/params/bootnodes.go

// MainnetBootnodes are the enode URLs of the P2P bootstrap nodes running on
// the main Ethereum network.
var MainnetBootnodes = []string{

    // Ethereum Foundation Go Bootnodes
    "enode://a979fb575495b8d6db44f750317d0f4622bf4c2aa3365d6af7c284339968eef29b69ad0dce72a4d8db5ebb4968de0e3bec910127f134779fbcb0cb6d3331163c@52.16.188.185:30303", // IE
    "enode://3f1d12044546b76342d59d4a05532c14b85aa669704bfe1f864fe079415aa2c02d743e03218e57a33fb94523adb54032871a6c51b2cc5514cb7c7e35b3ed0a99@13.93.211.84:30303",  // US-WEST
    "enode://78de8a0916848093c73790ead81d1928bec737d565119932b98c6b100d944b7a95e94f847f689fc723399d2e31129d182f7ef3863f2b4c820abbf3ab2722344d@191.235.84.50:30303", // BR
    "enode://158f8aab45f6d19c6cbf4a089c2670541a8da11978a2f90dbf6a502a4a3bab80d288afdbeb7ec0ef6d92de563767f3b1ea9e8e334ca711e9f8e2df5a0385e8e6@13.75.154.138:30303", // AU
    "enode://1118980bf48b0a3640bdba04e0fe78b1add18e1cd99bf22d53daac1fd9972ad650df52176e7c7d89d1114cfef2bc23a2959aa54998a46afcf7d91809f0855082@52.74.57.123:30303",  // SG

Parity: https://github.com/paritytech/parity/blob/b50fb71dd1d29dfde2a6c7e1830447cf30896c31/ethcore/res/ethereum/morden.json

these nodes indicates to yours the others nodes available to connect to. However the nodes could discover the others based on the ethereum discovery protocol : https://github.com/ethereum/wiki/wiki/Node-discovery-protocol